High performance catadioptric imaging system

ABSTRACT

A reduced size catadioptric objective and system is disclosed. The objective may be employed with light energy having a wavelength in the range of approximately 190 nanometers through the infrared light range. Elements are less than 100 mm in diameter. The objective comprises a focusing lens group configured to receive the light energy and comprising at least one focusing lens. The objective further comprises at least one field lens oriented to receive focused light energy from the focusing lens group and provide intermediate light energy. The objective also includes a Mangin mirror arrangement positioned to receive the intermediate light energy from the field lens and form controlled light energy for transmission to a specimen. The Mangin mirror arrangement imparts controlled light energy with a numerical aperture in excess of 0.65 and up to approximately 0.90, and the design may be employed in various environments.

[0001] This application claims the benefit of U.S. Provisional PatentApplication Serial No. 60/449,326, entitled “High Performance, Low CostCatadioptric Imaging System,” filed Feb. 21, 2003.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to the field of opticalimaging and more particularly to catadioptric optical systems used formicroscopic imaging, inspection, and lithography applications.

[0004] 2. Description of the Related Art

[0005] Many optical and electronic systems exist to inspect surfacefeatures for defects such as those on a partially fabricated integratedcircuit or a photomask. Defects may take the form of particles randomlylocalized on the surface, scratches, process variations, and so forth.Such techniques and devices are well known in the art and are embodiedin various commercial products such as those available from KLA-TencorCorporation of San Jose, Calif.

[0006] Specialized optical systems are required in inspection devices toenable imaging of defects found on semiconductor wafers and photomasks.Improved performance for such systems may be realized using speciallydesigned components that facilitate beneficial inspection parameters,such as high numerical apertures. The numerical aperture of an objectiverepresents the objective's ability to collect light and resolve finespecimen detail at a fixed object distance. Numerical aperture ismeasured as the sine of the vertex angle of the largest cone ofmeridional rays that can enter or leave the optical system or element,multiplied by the refractive index of the medium in which the vertex ofthe cone is located. A large numerical aperture provides distinctadvantages during inspection, not the least of which is an ability toresolve smaller features of the specimen. Also, high NAs collect alarger scattering angle, thereby tending to improve performance indarkfield environments over systems having relatively low NAs. Twopatents that disclose high numerical aperture (NA) catadioptric systemsare U.S. Pat. No. 5,717,518 to Shafer et al. and U.S. Pat. No. 6,483,638to Shafer et al. A representative illustration of a catadioptric design100 in accordance with the teachings of the '518 patent is presented inFIG. 1, which is similar to FIG. 1 of the '518 patent. A representativeillustration of a catadioptric design 200 in accordance with theteachings of the '638 patent is presented in FIG. 2, which hassimilarities to FIG. 4 of the '638 patent.

[0007] U.S. Pat. No. 5,717,518 to Shafer et al. discloses an imagingdesign capable of high NA, ultra broadband UV imaging. The high NA (upto approximately 0.9) system can be used for broadband bright field andmultiple wavelength dark-field imaging. Certain issues exist withdesigns similar to that presented in FIG. 1. First, the field lens groupmay need to be physically located within a central hole in the largecurved catadioptric element, which can make manufacturing very difficultand extremely expensive. Second, the field lens elements in such adesign may require at least one glued interface. In the presence ofwavelengths less then 365 nm, reliable glues that can withstand lightintensity levels at an internal focus are generally unavailable. Third,the lens elements in such a design may be located very close to a fieldplane, thereby requiring a high degree of, or nearly perfect, surfacequality and bulk material quality to prevent image degradation. Fourth,element diameters are typically larger than a standard microscopeobjective, especially for the catadioptric group. Large diameterelements frequently make integration into an inspection system difficultand can increase manufacturing costs.

[0008] The design of FIG. 2 is generally capable of high NA, ultrabroadband UV imaging. The design is a high NA (up to approximately 0.9)imaging system that can be used for broadband bright field and multiplewavelength dark-field imaging and can use a varifocal tube lens toprovide a large range of magnifications. The FIG. 2 design introducesvery tight tolerances in the field lens group, due in part to increasedon-axis spherical aberration produced by the catadioptric group. Thison-axis spherical aberration must be corrected by the followingrefractive lens elements. The design of FIG. 2 is relatively large,thereby generally requiring complicated optomechanical mounting ofelements, especially in the catadioptric group.

[0009] Other optical arrangements have been developed to performspecimen inspection, but each arrangement tends to have certain specificdrawbacks and limitations. Generally, in a high precision inspectionenvironment, an objective with a short central wavelength providesadvantages over those with long central wavelengths. Shorter wavelengthscan enable higher optical resolution and improved defect detection, andcan facilitate improved defect isolation on upper layers of multi-layerspecimens, such as semiconductor wafers. Shorter wavelengths can provideimproved defect characterization. An objective that can cover as large awavelength range as possible may also be desirable, particularly whenusing an arc lamp as an illumination source. An all refractive objectivedesign is difficult in this wavelength range because few glass materialshaving high transmission are effective for chromatic correction. A smallbandwidth may not be desirable for inspection applications due tolimitation of available light power and increased interference from thinfilms on the surface being inspected.

[0010] A large field size can provide distinct advantages duringinspection. One advantage is an ability to scan a larger area of thespecimen in a given period of time, thereby increasing throughput,measured as the ability to scan a large area over a small period oftime. A relatively large field size in a typical design in this type ofenvironment can be approximately or greater than 0.2 mm using an imagingmagnification of 200× to support a sensor with an 40 mm diagonal. Smallobjectives are also desirable, as small objectives can be used incombination with standard microscope objectives and fit in standardmicroscope turrets. The standard objective flange to object length is 45mm, while certain objectives employ lens diameters greater than 100 mmhaving length of over 100 mm. Other smaller catadioptric objectives havebeen produced, but still typically have lens diameters in excess of 60mm and length over 60 mm. Certain of these smaller objectives have NAslimited to 0.75 and field sizes limited to 0.12 mm with a bandwidth lessthan 10 nm. Such designs typically use a Schwartzchild approach withlenses added within the catadioptric group in an effort to improveperformance. Working distances are typically greater than 8 mm. Thisdesign approach can somewhat reduce the objective diameter, at the costof increasing central obscuration, significantly degrading objectiveperformance.

[0011] An objective having low intrinsic aberrations is also desirable,as is an objective that is largely self-corrected for both monochromaticand chromatic aberrations. A self corrected objective will have looseralignment tolerances with other self corrected imaging optics. Anobjective with loose manufacturing tolerances, such as lens centeringtolerances, may be particularly beneficial. Further, reducing incidenceangles on lens surfaces can have a large effect on optical coatingperformance and manufacturing. In general, lower angles of incidence onlens surfaces also produce looser manufacturing tolerances.

[0012] It would be beneficial to provide a system overcoming thesedrawbacks present in previously known systems and provide an opticalinspection system design having improved functionality over devicesexhibiting those negative aspects described herein.

SUMMARY OF THE INVENTION

[0013] According to a first aspect of the present design, there isprovided an objective employed for use with light energy having awavelength in the range of approximately 285 to 320 nanometers. Theobjective comprises a focusing lens group comprising at least onefocusing lens configured to receive the light energy, a field lensoriented to receive focused light energy from the focusing lens groupand provide intermediate light energy, and a Mangin mirror arrangementpositioned to receive the intermediate light energy from the field lensand form controlled light energy. A ratio of lens diameter for a largestelement of all focusing lenses, the field lens, and the Mangin mirrorarrangement to field size is less than 100 to 1.

[0014] According to a second aspect of the present design, there isprovided an objective employed for use with light energy having awavelength in the range of approximately 157 nanometers through theinfrared light range. The objective comprises a focusing lens groupconfigured to receive the light energy and comprising at least onefocusing lens, at least one field lens oriented to receive focused lightenergy from the focusing lens group and provide intermediate lightenergy, and a Mangin mirror arrangement positioned to receive theintermediate light energy from the field lens and form controlled lightenergy. The Mangin mirror arrangement imparts controlled light energy toa specimen with a numerical aperture in excess of 0.65, wherein eachlens employed in the objective and each element in the Mangin mirrorarrangement has diameter less than 100 millimeters.

[0015] According to a third aspect of the present design, there isprovided an objective constructed of a single glass material for usewith light energy having a wavelength in the range of approximately 157nanometers through the infrared light range. The objective comprises atleast one focusing lens having diameter less than approximately 100millimeters receiving the light energy and transmitting focused lightenergy, at least one field lens having diameter less than approximately100 millimeters, receiving the focused light energy and transmittingintermediate light energy, and at least one Mangin mirror element havingdiameter less than 100 millimeters receiving the intermediate lightenergy and providing controlled light energy to a specimen.

[0016] According to a fourth aspect of the present design, there isprovided a system for imaging a specimen using light energy in the rangeof 157 nanometers through the infrared light range. The system comprisesa plurality of lenses having diameter of less than approximately 25millimeters receiving the light energy and providing intermediate lightenergy, and a Mangin mirror arrangement receiving the intermediate lightenergy and providing controlled light energy to the specimen.

[0017] According to a fifth aspect of the present design, there isprovided a catadioptric objective comprising a catadioptric groupcomprising at least one element configured to receive light energy froma specimen and providing reflected light energy forming reflected lightenergy, a field lens group comprising at least one field lens receivingthe reflected light energy and transmitting resultant light energy, anda focusing lens group comprising at least one focusing lens receivingresultant light energy and transmitting focused resultant light energy,wherein an imaging numerical aperture for the objective is at least0.65, the objective having a maximum lens diameter for all lensesemployed and a field size, and wherein the ratio of maximum lensdiameter to field size is less than 100 to 1.

[0018] According to a sixth aspect of the present design, there isprovided a method of imaging a specimen. The method comprises focusingreceived light energy using a focusing lens group, receiving focusedlight energy and providing intermediate light energy using a field lensgroup, and receiving intermediate light energy and forming controlledlight energy using a Mangin mirror arrangement. A field size is formedusing the focusing lens group, the field lens group, and the Manginmirror arrangement, and a ratio of a largest element in the focusinglens group, field lens group, and Mangin mirror arrangement to fieldsize is less than 100 to 1.

[0019] According to a seventh aspect of the present design, there isprovided an objective comprising means for focusing received lightenergy using a focusing lens group, means for receiving focused lightenergy and providing intermediate light energy using a field lens group,and means for receiving intermediate light energy and forming controlledlight energy using a Mangin mirror arrangement. A field size is formedusing the focusing lens group, the field lens group, and the Manginmirror arrangement, and a ratio of a largest element in the focusinglens group, field lens group, and Mangin mirror arrangement to fieldsize is less than 100 to 1.

[0020] According to an eighth aspect of the present design, there isprovided an objective employed for use with light energy having awavelength in the range of approximately 157 nanometers through theinfrared light range. The objective comprises focusing means forreceiving the light energy and providing focused light energy, fieldlensing means for receiving focused light energy from the focusing meansand providing intermediate light energy, and mirror means for receivingthe intermediate light energy from the field lensing means and formingcontrolled light energy, the mirror means imparting the controlled lightenergy to a specimen with a numerical aperture in excess of 0.65,wherein each lens employed in the objective and each element in themirror means has diameter less than 100 millimeters.

[0021] These and other objects and advantages of the present inventionwill become apparent to those skilled in the art from the followingdetailed description of the invention and the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 illustrates an aspect of the catadioptric objective designsimilar to that presented in FIG. 1 of U.S. Pat. No. 5,717,518;

[0023]FIG. 2 is an aspect of the catadioptric objective design similarto that presented in FIG. 4 of U.S. Pat. No. 6,483,638;

[0024]FIG. 3 presents a reduced size catadioptric objective with a highNA in accordance with the present invention;

[0025]FIG. 4 is a size comparison between the objective of the designpresented in FIG. 2, the reduced size catadioptric objective of FIG. 3,and a standard microscope objective;

[0026]FIG. 5A is a graph of decenter sensitivity for the objectivedesign of FIG. 3;

[0027]FIG. 5B presents a sensitivity comparison between the design ofFIG. 3, a UV refractive objective corrected from 365-436 nm, and acatadioptric objective based on the design of FIG. 2;

[0028]FIG. 6 is an alternate aspect of the reduced size catadioptricobjective in accordance with the present invention;

[0029]FIG. 7A illustrates a tube lens arrangement in accordance with thepresent invention;

[0030]FIG. 7B illustrates an objective and tube lens corrected from266-405 nm with a 0.4 mm diameter field;

[0031]FIG. 7C illustrates an objective design with a 1 mm field size anddiameter of approximately 58 mm;

[0032]FIG. 8 is a design able to perform in the presence of wavelengthsfrom approximately 311-315 nm, having approximately 26 mm diameter, afield size of approximately 0.28 mm, and NA of approximately 0.90;

[0033]FIG. 9 is an approximately 0.28 mm field design havingapproximately 26 mm diameter, a wavelength of between approximately 297and 313 nm, and NA of approximately 0.90;

[0034]FIG. 10 is an approximately 0.4 mm field design havingapproximately 26 mm diameter, a wavelength of between approximately 297and 313 nm, and NA of approximately 0.90;

[0035]FIG. 11 illustrates a broad band design having approximately 26 mmdiameter, a wavelength of between approximately 266 and 313 nm, fieldsize of approximately 0.28 mm, and NA of approximately 0.90; and

[0036]FIG. 12 is a graph comparing relative bandwidth versus the maximumlens element diameter of certain designs, including the current design;and

[0037]FIG. 13 is a graph comparing field size versus the maximum lenselement diameter of certain designs, including the present design.

DETAILED DESCRIPTION OF THE INVENTION

[0038] According to the present invention, there is provided acatadioptric objective corrected over a wavelength range from 285-320 nmusing a single glass material, or in certain circumstances, more thanone glass material to improve performance. One aspect of the objectivedesign is shown in FIG. 3. The catadioptric objective as shown in FIG. 3is optimized for broad-band imaging in the UV spectral region, namelyapproximately 0.285 to 0.320 micron wavelengths. The objective providesrelatively high numerical apertures and large object fields. Theinventive design presented uses the Schupmann principle in combinationwith an Offner field lens to correct for axial color and first orderlateral color. As shown in the aspect presented in FIG. 3, the fieldlens group 305 is slightly displaced from the intermediate image 306 toobtain enhanced performance.

[0039] From FIG. 3, the catadioptric group 301 or Mangin mirrorarrangement includes a Mangin mirror element 302. Mangin mirror element302 is a reflectively coated lens element. The catadioptric group 301also includes and a concave spherical reflector 303, also a reflectivelycoated lens element. Both elements in the catadioptric group 301 havecentral optical apertures where reflective material is absent. Thisallows light to pass from the object or specimen 300 (not shown) throughMangin mirror element 302, reflect from the second or inner surface ofconcave spherical reflector 303, onto the reflective surface 320 ofMangin mirror element 302, and through concave spherical reflector 303to form an intermediate image 306 between concave spherical reflector303 and field lens group 304. The field lens group 304 may comprise oneor more lenses, and in the aspect shown in FIG. 3, one field lens isemployed in the field lens group 304.

[0040] The focusing lens group 307 uses multiple lens elements, in theaspect shown six lens elements 308, 309, 310, 311, 312, and 313. Alllenses in the focusing lens group 307 may be formed from a single typeof material to collect the light from the field lens group 304 and theintermediate image 306.

[0041] The lens prescription for the aspect of the invention illustratedin FIG. 3 is presented in Table 1. TABLE 1 Prescription for lenses forthe design of FIG. 3 Surface Number Radius Thickness Glass Diameter OBJInfinity Infinity 0 1 Infinity 15.50165 9.39467 STO Infinity −15.50165 83 53.51878 2 Fused Silica 9.376161 4 −18.17343 0.976177 9.234857 510.48757 1.249953 Fused Silica 8.151456 6 5.891816 3.328088 7.199539 7−5.254784 5.105439 Fused Silica 7.084075 8 −8.860388 0.5 9.430437 912.82516 2 Fused Silica 9.711337 10 61.04848 0.5 9.468601 11 8.8925551.75 Fused Silica 9.125279 12 15.75614 2.126452 8.563035 13 7.216376 2Fused Silica 7.4431 14 21.90145 5.382485 6.702302 15 2.321495 1.3 FusedSilica 2.530266 16 13.47255 0.669203 1.651874 17 Infinity 0.4988650.711891 18 17.99728 3.170995 Fused Silica 25 19 13.41607 6.08537 21 20972.9414 5.220004 Fused Silica 20.5 21 −78 −5.220004 MIRROR 20.5 22972.9414 −6.08537 20.5 23 13.41607 −3.170995 Fused Silica 21 24 17.997283.170995 MIRROR 25 25 13.41607 6.08537 21 26 972.9414 5.220004 FusedSilica 20.5 27 −78 0.3 20.5 IMA Infinity 0.410191

[0042] As may be appreciated by one skilled in the art, the numbers inthe leftmost column of Table 1 represent the surface number countingsurfaces from the left of FIG. 3. For example, the left surface of lens308 in the orientation presented in FIG. 3 (surface 3 in Table 1) has aradius of curvature of 53.51878 mm, a thickness of 2 mm, and therightmost surface (surface 4) has a radius of curvature of −18.17343 mm,and is 0.976177 mm from the next surface. The material used is fusedsilica, and the diameter of the left surface is 9.376161 mm and of theright surface is 9.234857 mm.

[0043] In the design presented in FIG. 3, the numerical aperture mayapproach or even exceed approximately 0.90. The design presented herein,including the aspect illustrated in FIG. 3, provides a maximum numericalaperture in all cases in excess of 0.65.

[0044] From FIG. 3, the focusing lens group 307 has the ability toreceive light energy and transmit focused light energy. The field lensgroup 304 has the ability to receive the focused light energy andprovide intermediate light energy, and form intermediate image 306. Thecatadioptric group or Mangin mirror arrangement 301 receives theintermediate energy and provides controlled light energy to thespecimen. Alternately, the reflected path originates at the specimen,and light reflected from the specimen is received by the catadioptricgroup or Mangin mirror arrangement 301 and forms and transmits reflectedlight energy. The field lens group 304 receives the reflected lightenergy and transmitting resultant light energy, and the focusing lensgroup receives resultant light energy and transmits focused resultantlight energy.

[0045] The design presented in FIG. 3 and Table 1 thus uses a singleglass material, fused silica. Other materials may be employed, but it isnoted that fused silica or any material used within the design mayrequire low absorption over a wide range of wavelengths from 190 nmthrough the infrared wavelength. Use of fused silica can enable thedesign to be re-optimized for any center wavelength in this wavelengthrange. For example, the design can be optimized for use with lasers at193, 198.5, 213, 244, 248, 257, 266, 308, 325, 351, 355, or 364nm. Thedesign can also be optimally employed to cover lamp spectral bands from192-194, 210-216, 230-254, 285-320, and 365-546 nm. In addition, ifcalcium fluoride is employed as the glass or lens material, the designcan be employed with an excimer laser at 157 nm or excimer lamps at 157or 177 nm. Re-optimization requires tuning or altering components withinthe abilities of those skilled in the art. Calcium fluoride lenses mayalso be employed in the field lens group to increase the bandwidth ofthe objective, a modification discussed generally in U.S. Pat. No.5,717,518.

[0046] As noted in FIG. 3, the objective has a diameter of 26millimeters, which is significantly smaller than objectives previouslyemployed in this wavelength range. The small size of this objective isparticularly beneficial in view of the performance characteristics ofthe objective. The objective can be mounted in a standard microscopeturret with a 45 mm flange-to-object separation. The objective supportsa numerical aperture of approximately 0.90, a field size ofapproximately 0.4 mm, has a corrected bandwidth from approximately285-313 nm, and a polychromatic wavefront error of less thanapproximately 0.038 waves. A size comparison between the objective ofthe design presented in FIG. 2, the design of FIG. 3, and a standardmicroscope objective is shown in FIG. 4.

[0047] As is true with any optical design, certain tradeoffs may be madeto improve performance characteristics depending on the desiredapplication of the objective or optical design. It is possible, forexample, to sacrifice bandwidth, field size, numerical aperture, and/orobjective size to enhance one of the aforementioned performancecharacteristics, depending on the application. For example, optimizingfor lower or higher NAs is possible. Reducing the NA can reduce themanufacturing tolerance and the outer diameter of the objective. LowerNA designs can provide larger field sizes and larger bandwidths. LowerNA designs with the same performance and less optical elements are alsopossible. Optimizing for higher NAs is also possible. Optimizing thedesign for higher NAs would generally limit the field size or bandwidthand may require slightly increased diameter objective elements.

[0048] The design of FIG. 3 has a field size of 0.4 mm in diameter. Sucha relatively large field size can support a large high speed sensor. Forexample, using an imaging magnification of 200×, a sensor having an 80mm diagonal can be supported. The design of FIG. 3 can also be extendedto larger field sizes by allowing larger lens diameters andre-optimizing the elements, again a task within the range of thoseskilled in the art.

[0049] The design of FIG. 3 has a relatively low intrinsic polychromaticwavefront aberration over the design bandwidth from approximately285-320 nm. The low wavefront aberration provides increasedmanufacturing headroom, or ease of manufacture, while enablingrelatively high performance of the manufactured objective. The design ofFIG. 3 provides good performance over narrow bands from approximately266 to 365 nm if the objective is refocused, again a task that may bereadily performed by one of ordinary skill in the art. Use of theobjective of FIG. 3 in this narrow band range allows use of lasers ornarrow lamp spectra, such as the 365 nm line of lasers. The design isalso self corrected. Self corrected in this context means that theobjective does not require any additional optical components to correctaberrations in order to achieve the design specifications. The abilityto self-correct tends to simplify optical testing metrology and opticalalignment to other self corrected imaging optics. Further correction ofresidual aberrations using additional imaging optics is also possible.Further aberration correction can increase optical specifications suchas bandwidth or field size.

[0050] One advantage of the present design is relatively loosemanufacturing tolerances. Specifically, the decenter tolerances ofindividual lenses are relatively loose. Having loose decenter tolerancesfor individual lens elements tends to simplify the manufacturingrequirements of the system. Any lens decenters encounterd duringmanufacturing may cause on-axis coma, a phenomenon that can be difficultto compensate without introducing other residual aberrations. Using thepresent design, it is possible to reduce the decenter sensitivity of thelens and mirror elements by carefully balancing the aberrations withinthe catadioptric group 301 and focusing lens group 307. Totalaberrations of the catadioptric group may be optimized using the designof FIG. 3 to balance the compensation required by the field lens group304 and focusing lens group 307. FIG. 5A shows the decenter sensitivityfor the objective. A 10 micron decenter, without using any compensators,introduces less than approximately 0.2 waves of aberration in allelements except lens 302. A 10 micron decenter without compensatorsintroduces approximately 0.29 waves of aberration. In the designpresented in FIG. 3, average tolerance is approximately 0.13 waves oferror at approximately 313 nm. Further balancing the tolerances on theelements in the catadioptric group 301 is also possible.

[0051] The decenter tolerances also scale with the wavelength beingused. This is because the optical path errors introduced for smalldecenters are not a strong function of wavelength. For example, if a 10micron decenter introduces 0.2 waves of aberration at a 266 nmwavelength, this is equivalent to a 0.0532 micron optical path error.The system operating at 365 nm would only introduce 0.15 waves ofaberration for the same decenter. This would have the same 0.0532 micronoptical path error.

[0052] These tolerances tend to be looser than other catadioptricdesigns in similar environments, and tend to be looser than moststandard refractive objective designs. FIG. 5B presents a sensitivitycomparison between the design of FIG. 3, a UV refractive objectivecorrected from 365-436 nm, and a catadioptric objective based on thedesign shown in FIG. 2. Generally, in the plots of FIG. 5B, a valuelower on the vertical scale indicates a more desirable design. Wavefronterror is plotted for a 10 micron decenter for each element withoutcompensation. Average sensitivity is less than the refractive objectiveand much less than the sensitivity of the catadioptric objective designsimilar to that from the design of FIG. 2.

[0053] This design also has very loose tolerances on the index of theglass material. This is largely because the design is of a singlematerial and does not rely on the index difference of two differentglass materials to compensate for chromatic aberrations. This also makesthe design very insensitive to temperature changes. Standard designs usemultiple glass materials with different index profiles for colorcorrection. The index profile for each material changes differently withtemperature. This changes the chromatic correction for temperaturesother than the design temperature and reduces the performance.

[0054] The objective design presented herein can support various modesof illumination and imaging. Modes supported can include bright fieldand a variety of dark field illumination and imaging modes. Other modessuch as confocal, differential interference contrast, polarizationcontrast may also be supported using the present design.

[0055] Bright field mode is commonly used in microscope systems. Theadvantage of bright field illumination is the clarity of the imageproduced. Using bright field illumination with an objective such as thatpresented herein provides a relatively accurate representation of objectfeature size multiplied by the magnification of the optical system. Theobjective and optical components presented herein can be readily usedwith image comparison and processing algorithms for computerized objectdetection and classification. Brightfield mode typically uses a broadband incoherent light source, but it may be possible to use laserillumination sources using slightly modified illumination systemcomponents employing the design presented herein.

[0056] The confocal mode has been used for optical sectioning to resolveheight differences of object features. Most imaging modes havedifficulty detecting changes in the height of features. The confocalmode forms separate images of object features at each height ofinterest. Comparison of the images then shows the relative heights ofdifferent features. Confocal mode may be employed using the designpresented herein.

[0057] Dark field mode has been used to detect features on objects. Theadvantage of the dark field mode is that flat specular areas scattervery little light toward the detector, resulting in a dark image.Surface features or objects protruding above the object tend to scatterlight toward the detector. Thus, in inspecting objects likesemiconductor wafers, dark field imaging produces an image of features,particles, or other irregularities on a dark background. The presentdesign may be employed with dark field mode illumination. Dark fieldmode provides a large resultant signal upon striking small features thatscatter light. This large resultant signal allows larger pixels to beemployed for a given feature size, permitting faster object inspections.Fourier filtering can also be used to minimize the repeating patternsignal and enhance the defect signal to noise ratio during dark fieldinspection.

[0058] Many different dark field modes exist, each including a specificillumination and collection scheme. Illumination and collection schemescan be chosen such that the scattered and diffracted light collectedfrom the object provides an acceptable signal-to-noise ratio. Certainoptical systems use different dark field imaging modes including ringdark field, laser directional dark field, double dark field, and centraldark ground. Each of these dark field imaging modes may be employed inthe present design.

[0059] An alternate aspect of the present design presents an objectivewith increased bandwidth. This aspect of the design is presented in FIG.6. The main difference between the design of FIG. 6 and that of FIG. 3is the tradeoff between bandwidth and field size. The objective of thedesign of FIG. 6 is corrected over a broader bandwidth from 266 to 320nm but has a relatively smaller field, approximately 0.28 mm, ascompared with the 0.4 mm of the design of FIG. 3. The design of FIG. 6maintains the high approximately 0.90 numerical aperture. The worst casepolychromatic wavefront error for the FIG. 6 design is approximately0.036 waves.

[0060] From FIG. 6, the catadioptric group 601 includes a Mangin mirrorelement 602, which is a reflectively coated lens element, and a concavespherical reflector 603, which is also a reflectively coated lenselement. Both Mangin mirror element 602 and concave spherical reflector603 have central optical apertures where reflective material is absent.The absence of reflective material, in the center of the componentsshown, allows light to pass from the object or specimen 600 (not shown)through Mangin mirror element 602, reflect from the second surface ofconcave spherical reflector 603 onto the Mangin mirror element 602, andtransmit through concave spherical reflector 603 to form an intermediateimage 620 between concave spherical reflector 603 and field lens group604, comprising a single field lens 615 in this aspect of the design.

[0061] The focusing lens group 605 employs multiple lens elements, inthis aspect the six lens elements 606, 607, 608, 609, 610, and 611,which may all be formed from a single type of material. The focusinglens group 605 collects light from the field lens group 604, includingthe intermediate image 620.

[0062] The design presented in FIG. 6 has the advantages and flexibilitydescribed with respect to the design of FIG. 3. The lens prescriptionfor this embodiment is shown in Table 2. TABLE 2 Prescription for lensesfor the design of FIG. 6 Surf Radius Thickness Glass Diameter OBJInfinity Infinity 0  1 Infinity 16.20723 9.020484 STO Infinity −16.207238  3 64.63011 2 FUSED SILICA 9.010584  4 −19.00905 1.675169 8.894847  510.3536 1.249991 FUSED SILICA 7.776084  6 5.91317 3.249904 6.942948  7−5.240171 5.243182 FUSED SILICA 6.855225  8 −9.11876 0.5 9.288367  916.20784 2 FUSED SILICA 9.638653 10 Infinity 0.5 9.499901 11 8.9514383.573584 FUSED SILICA 9.210718 12 12.83071 0.5 7.808034 13 7.107306 2FUSED SILICA 7.502914 14 29.37779 5.583862 6.837774 15 2.252897 1.3FUSED SILICA 2.391106 16 11.8636 0.668164 1.486574 17 Infinity 0.4997420.548495 18 17.95894 3.09472 FUSED SILICA 25 19 13.41421 6.156826 21 201134 5.204856 FUSED SILICA 20.5 21 −78 −5.204856 MIRROR 20.5 22 1134−6.156826 20.5 23 13.41421 −3.09472 FUSED SILICA 21 24 17.95894 3.09472MIRROR 25 25 13.41421 6.156826 21 26 1134 5.204856 FUSED SILICA 20.5 27−78 0.3 20.5 IMA Infinity 0.289101

[0063] A further aspect of the present design uses a tube lens tocorrect for residual aberrations in the objective. Residual aberrationsare primarily the chromatic variation of distortion and higher orderlateral color. These residual aberrations are related to use of theOffner field lens in the objective. One method to correct these residualaberrations is to employ a second glass material in the Offner fieldlens. Use of a second material can lead to an optical design with largeelements and relatively tight tolerances. The alternative approachpresented in this design is to use additional imaging optics to correctfor residual aberrations. Such a design can produce a system having highNA, large field size, small lens diameter, as well as relatively loosetolerances.

[0064] Correcting these residual aberrations can further increase thefield size or increase the bandwidth while maintaining the field size.The design of FIG. 7A maintains the same approximately 0.4 mm field sizeas in the design of FIG. 3 and extends the bandwidth to cover 266 to 365nm without need for refocusing. The worst case polychromatic wavefronterror for the design of FIG. 7A is approximately 0.036 waves.

[0065] The design includes two air spaced doublets 701, 702, 703, and704, the doublets 701-704 fashioned from fused silica and calciumfluoride. The doublets 701-704 focus light through three fused silicalens elements, namely lens elements 705, 706, and 707. these lenselements 705-707 are in proximity to an internal field. Light is thencollimated by an air spaced triplet 708, 709, and 710. Light then formsan external pupil at 711. The external pupil 711 can be used for placingdark field apertures, Fourier filters, and beamsplitters.

[0066] The lens prescription for the aspect of the invention illustratedin FIG. 7A is shown in Table 3. TABLE 3 Prescription for lenses for thedesign of FIG. 7A Surf Radius Thickness Glass Diameter OBJ Infinity 0.30.4 1 78 5.155765 FUSED SILICA 21 2 −1031.094 6.132752 21 3 −13.387663.334036 FUSED SILICA 21.5 4 −18.2281 −3.334036 MIRROR 25.5 5 −13.38766−6.132752 21.5 6 −1031.094 −5.155765 FUSED SILICA 21 7 78 5.155765MIRROR 21 8 −1031.094 6.132752 21 9 −13.38766 3.334036 FUSED SILICA 21.510 −18.2281 0.598511 25.5 11 Infinity 0.595647 0.87265 12 −22.673641.496994 FUSED SILICA 1.716759 13 −2.487035 5.332021 2.721696 14−24.12325 1.749722 FUSED SILICA 6.761726 15 −8.563906 1.647307 7.42632216 Infinity 1.017137 8.707626 17 −23.20559 1.75 FUSED SILICA 9.034138 18−10.09888 0.499806 9.544791 19 459.357 2 FUSED SILICA 10.00487 20−12.90167 0.499731 10.16545 21 9.888518 5.284916 FUSED SILICA 9.73846922 5.468369 3.606566 7.299015 23 −6.158311 1.499744 FUSED SILICA7.434168 24 −10.89758 0.499623 8.474502 25 18.52911 2 FUSED SILICA9.287792 26 −68.1321 −15.25736 9.417208 STO Infinity 15.25736 8.09706 28Infinity 34.89506 9.431455 29 — 0 — 30 Infinity 6 FUSED SILICA 18.4614331 Infinity 0 25.39024 32 — 0 −— 33 Infinity 30 17.16851 34 — 0 — 35Infinity 6 FUSED SILICA 26.81778 36 Infinity 0 20.63295 37 — 0 — 38Infinity 81 15.2277 39 −159.7003 4 FUSED SILICA 22.27788 40 37.473860.999856 22.92295 41 33.36497 9 CAF2 23.58799 42 −80.14523 3.43644224.07579 43 38.4464 8 CAF2 23.97432 44 −53.0633 1.5 22.95647 45−39.45511 3 FUSED SILICA 22.35342 46 1094.058 43.27621 21.67501 4710.8487 3.18507 FUSED SILICA 12.40192 48 8.96916 4.999989 10.71199 49−24.58978 2.5 FUSED SILICA 10.26452 50 117.1346 47.95638 10.34545 51175.9777 5 FUSED SILICA 16.71625 52 −37.37344 74.18151 17.10185 53−1113.4 5 CAF2 11.5593 54 −14.94822 0.99955 11.38304 55 −13.4032 2 FUSEDSILICA 10.93698 56 18.26209 0.99969 10.92178 57 17.51017 6 CAF2 11.2519958 −33.75194 38.51994 11.218 59 — 100 4.910667 IMA Infinity 16.34334

[0067] The tube lens design of FIG. 7A uses only fused silica andcalcium fluoride. Both of these materials have transmissions fromapproximately 190 nm through the infrared. Thus a tube lens can bedesigned to operate with an objective that can be re-optimized fordifferent center wavelengths. Other tube lens magnifications may beachieved using this design. The design of FIG. 7A can be re-optimizedfor different afocal magnifications depending on the desired overallmagnification. Using the design presented herein, a focusing tube lensthat directly forms an image that can expose a high speed sensor may berealized.

[0068] An additional aspect of the present design uses a tube lens tocorrect for residual aberrations in the objective. Correcting theseresidual aberrations can increase the field size or increase thebandwidth while maintaining the field size. Residual aberrations areprimarily the chromatic variation of distortion and higher order lateralcolor. The design of FIG. 7B maintains the same approximately 0.4 mmfield size as in the design of FIG. 3 and extends the bandwidth to cover266 to 405 nm without need for refocusing. The worst case polychromaticwavefront error for the design of FIG. 7B is approximately 0.041 waves.

[0069] The design in FIG. 7B is composed of an objective 751 thatcollects the light and a tube lens 753 that corrects residualaberations. A set of lenses 752 may be provided to enhance performance.To achieve additional bandwidth beyond the design of FIG. 7A, theobjective and tube lens of FIG. 7B are partially optimized together.Partial combined optimization of the objective and tube lens allows forfurther correction of the limiting off axis lateral color and chromaticvariation of distortion. The tube lens forms an external pupil 754 thatcan be used in the same fashion as the design of FIG. 7A. The designpresented in FIG. 7B also shows optional beamsplitter elements 754 thatcan be used to fold in illumination and autofocus light. The lensprescription for the aspect of the invention illustrated in FIG. 7B isshown in Table 4. TABLE 4 Prescription for lenses for the design of FIG.7B Surf Radius Thickness Glass Diameter OBJ Infinity 0.300 0.4 1 78.0005.168 Fused silica 21 2 −850.121 6.031 21 3 −13.361 3.505 Fused silica21.5 4 −18.352 −3.505 MIRROR 25.5 5 −13.361 −6.031 21.5 6 −850.121−5.168 Fused silica 21 7 78.000 5.168 MIRROR 21 8 −850.121 6.031 21 9−13.361 3.505 Fused silica 21.5 10 −18.352 0.599 25.5 11 Infinity 0.5980.8876633 12 −22.089 1.498 Fused silica 1.735372 13 −2.492 5.5252.742536 14 −25.242 1.750 Fused silica 6.958087 15 −8.752 1.574 7.613493STO Infinity 1.011 8.782304 17 −26.420 1.750 Fused silica 9.130406 18−10.453 0.500 9.615398 19 214.479 2.000 Fused silica 10.09149 20 −12.8580.500 10.245 21 10.710 5.074 Fused silica 9.775169 22 5.729 3.6227.468521 23 −6.365 1.499 Fused silica 7.601525 24 −11.721 0.499 8.66019525 20.390 2.000 Fused silica 9.505927 26 −47.176 −15.391 9.654623 27Infinity 15.391 8.373404 28 Infinity 40.197 9.675574 29 — 0.000 — 30Infinity 6.000 Fused silica 19.30992 31 Infinity 0.000 26.25127 32 —0.000 — 33 Infinity 30.000 17.76485 34 — 0.000 — 35 Infinity 6.000 Fusedsilica 27.58405 36 Infinity 0.000 21.36646 37 — 0.000 — 38 Infinity81.000 15.75755 39 −140.860 4.000 Fused silica 22.67915 40 35.044 1.06823.39086 41 31.623 9.000 CAF2 24.17115 42 −71.279 1.000 24.64826 4334.991 8.000 CAF2 24.5185 44 −50.752 1.500 23.4315 45 −37.766 3.000Fused silica 22.75917 46 331.537 39.138 21.89289 47 11.729 3.402 Fusedsilica 12.61895 48 9.275 6.254 10.82904 49 −22.713 2.500 Fused silica10.19172 50 149.521 45.554 10.31249 51 −142.117 5.000 Fused silica16.06325 52 −25.943 76.816 16.73351 53 −369.224 5.000 CAF2 11.62667 54−14.234 1.000 11.50051 55 −12.790 2.000 Fused silica 11.04605 56 20.3241.000 11.08561 57 18.583 5.500 CAF2 11.41199 58 −32.851 38.519 11.3976959 — 100.000 5.11369 IMA Infinity 16.29315

[0070] The design spectrum can be limited to 266-365 nm and reoptimizedfor a 0.5 mm field size. The tube lens design of FIG. 7B also uses onlyfused silica and calcium fluoride and has all the flexibility forreoptimizing presented for the design in FIG. 7A.

[0071] The maximum numerical apertures of the current designs approachesor exceeds 0.9. The numerical aperture of a design may be reduced byplacing a variable aperture at the aperture stop of the objective,effectively limiting the illumination and imaging light angles. It isalso possible to control illumination and imaging angles independentlyby placing apertures at an external pupil plane using imaging opticssuch as the tube lens designs in FIG. 7A or FIG. 7B. The numericalaperture of the illumination may be reduced by underfilling theobjective aperture with the illumination light. Such a design enablesthe full imaging NA to be used.

[0072] An alternate aspect of the current design is an objective withincreased field size. This aspect of the design is presented in FIG. 7C.The main difference between the design of FIG. 7C and that of FIG. 3 isthe increase field size from 0.4 mm to 1.0 mm and an increase in lensdiameter from 25 mm to 58 mm. In contrast, this field diameter is thesame as in the design of FIG. 2. Maximum lens diameter of this design ismuch smaller than the design of FIG. 2. The objective of the design ofFIG. 7C is corrected over a bandwidth from 285 to 320 nm, maintains thehigh 0.90 numerical aperture, and the worst case polychromatic wavefronterror for the FIG. 7C design is approximately 0.033 waves.

[0073] From FIG. 7C, the catadioptric group 771 includes a Mangin mirrorelement 772, which is a reflectively coated lens element, and a concavespherical reflector 773, which is also a reflectively coated lenselement. Both Mangin mirror element 772 and concave spherical reflector773 have central optical apertures where reflective material is absent.The absence of reflective material, in the center of the componentsshown, allows light to pass from the object or specimen 770 (not shown)through Mangin mirror element 772, reflect from the second surface ofconcave spherical reflector 773 onto the Mangin mirror element 772, andtransmit through concave spherical reflector 773 to form an intermediateimage 790 between concave spherical reflector 773 and field lens group774, comprising three field lens elements 783, 784, and 785 in thisaspect of the design.

[0074] The focusing lens group 775 employs multiple lens elements, inthis aspect the seven lens elements 776, 779, 780, 781, and 782, whichmay all be formed from a single type of material. The focusing lensgroup 775 collects light from the field lens group 774, including theintermediate image 790.

[0075] The design presented in FIG. 6 has the advantages and flexibilitydescribed with respect to the design of FIG. 3. The lens prescriptionfor this design is shown in Table 5. TABLE 5 Prescription for lenses forthe design of FIG. 7C Surf Radius Thickness Glass Diameter OBJ InfinityInfinity 0.000 1 Infinity 43.913 23.946 STO Infinity −43.913 20.000 3349.851 4.500 Fused silica 23.928 4 −43.383 0.500 23.709 5 30.361 3.650Fused silica 21.950 6 16.181 7.177 19.386 7 −17.138 7.305 Fused silica19.277 8 32.672 0.872 23.722 9 47.511 7.000 Fused silica 23.916 10−30.308 0.500 25.201 11 37.466 5.500 Fused silica 26.737 12 −147.45827.319 26.555 13 14.910 4.500 Fused silica 21.011 14 22.738 0.500 19.51515 20.121 5.000 Fused silica 19.161 16 −127.415 7.984 17.640 17 12.5782.500 Fused silica 7.187 18 −46.414 0.500 5.333 19 −12.279 3.131 Fusedsilica 4.668 20 −15.865 2.594 1.955 21 −576.001 2.250 Fused silica 4.51622 −20.181 0.250 6.277 23 40.385 6.603 Fused silica 60.000 24 29.57415.917 50.000 25 −777.423 10.056 Fused silica 50.000 26 −202.605 −10.056MIRROR 50.000 27 −777.423 −15.917 50.000 28 29.574 −6.603 Fused silica50.000

[0076] Further aspects of the design are presented in FIGS. 8-11, whereFIG. 8 is a design able to perform in the presence of wavelengths fromapproximately 311-315 nm, having approximately 26 mm diameter, a fieldsize approximately 0.28 mm, and NA of approximately 0.90. The lensprescription for this design is shown in Table 6. TABLE 6 Prescriptionfor lenses for the design of FIG. 8 Surf Radius Thickness Glass DiameterOBJ Infinity Infinity 0.000 1 Infinity 18.849 8.538 STO Infinity −18.8497.220 3 6.048 4.786 Fused silica 8.419 4 4.149 1.727 5.777 5 19.8602.000 Fused silica 5.724 6 −17.207 1.449 5.502 7 −3.955 1.200 Fusedsilica 5.247 8 −12.991 0.100 5.861 9 10.518 5.617 Fused silica 6.098 10−15.147 0.100 5.985 11 4.995 2.249 Fused silica 5.701 12 −159.821 0.9995.037 13 −5.316 4.092 Fused silica 4.659 14 −4.477 0.904 4.116 15 2.4481.906 Fused silica 2.619 16 4.138 0.248 1.101 17 Infinity 1.501 0.801 1816.697 2.750 Fused silica 25.240 19 13.901 7.871 22.000 20 −78.318 2.000Fused silica 22.000 21 −100.000 −2.000 MIRROR 22.000 22 −78.318 −7.87122.000 23 13.901 −2.750 Fused silica 22.000 24 16.697 2.750 MIRROR25.240 25 13.901 7.871 22.000 26 −78.318 2.000 Fused silica 21.000 27−100.000 0.200 22.000 IMA Infinity 0.291

[0077]FIG. 9 is an approximately 0.28 mm field design havingapproximately 26 mm diameter, a wavelength of between approximately 297and 313 nm, and NA of approximately 0.90. The lens prescription for thisdesign is shown in Table 7. TABLE 7 Prescription for lenses for thedesign of FIG. 9 Surf Radius Thickness Glass Diameter OBJ InfinityInfinity 0.000 1 Infinity 20.163 8.585 STO Infinity −20.163 7.170 3−115.896 1.750 Fused silica 8.591 4 −16.723 5.036 8.562 5 −8.430 2.000Fused silica 7.122 6 −9.664 0.100 7.349 7 11.608 1.200 Fused silica7.019 8 4.779 1.598 6.337 9 10.332 1.750 Fused silica 6.622 10 135.1621.719 6.592 11 −6.281 2.555 Fused silica 6.583 12 −9.052 0.100 7.587 135.854 3.250 Fused silica 7.900 14 −17.400 1.125 7.264 15 −7.026 1.499Fused silica 6.559 16 −8.971 5.055 6.242 17 2.951 1.906 Fused silica2.442 18 −21.084 0.500 1.255 19 Infinity 1.580 0.314 20 17.135 4.713Fused silica 26.000 21 12.147 6.064 20.000 22 −164.287 2.500 Fusedsilica 20.000 23 −100.000 −2.500 MIRROR 20.000 24 −164.287 −6.064 20.00025 12.147 −4.713 Fused silica 20.000 26 17.135 4.713 MIRROR 26.000 2712.147 6.064 20.000 28 −164.287 2.500 Fused silica 20.000 29 −100.0000.200 20.000 IMA Infinity 0.280

[0078]FIG. 10 is an approximately 0.4 mm field design havingapproximately 26 mm diameter, a wavelength of between approximately 297and 313 nm, and NA of approximately 0.90. The lens prescription for thisdesign is shown in Table 8. TABLE 8 Prescription for lenses for thedesign of FIG. 10 Surf Radius Thickness Glass Diameter OBJ InfinityInfinity 0.000 1.000 Infinity 17.977 8.974 STO Infinity −17.977 7.1713.000 −73.415 1.750 Fused silica 8.988 4.000 −16.484 3.889 8.954 5.000−7.914 3.077 Fused silica 7.822 6.000 −8.792 0.103 8.317 7.000 10.9841.200 Fused silica 7.777 8.000 4.966 1.460 6.942 9.000 9.494 1.500 Fusedsilica 7.137 10.000 23.256 2.020 7.037 11.000 −6.669 1.871 Fused silica7.044 12.000 −10.034 0.100 7.866 13.000 6.034 2.500 Fused silica 8.34414.000 66.970 0.100 7.904 15.000 12.304 1.750 Fused silica 7.531 16.000−60.162 1.300 6.846 17.000 −6.852 1.499 Fused silica 6.139 18.000 −8.9934.511 5.804 19.000 3.141 1.750 Fused silica 2.466 20.000 −15.561 0.4991.420 21.000 Infinity 1.841 0.794 22.000 17.138 4.708 Fused silica26.000 23.000 12.005 6.070 20.000 24.000 −177.009 2.500 Fused silica20.000 25.000 −100.000 −2.500 MIRROR 20.000 26.000 −177.009 −6.07020.000 27.000 12.005 −4.708 Fused silica 20.000 28.000 17.138 4.708MIRROR 26.000 29.000 12.005 6.070 20.000 30.000 −177.009 2.500 Fusedsilica 20.000 31.000 −100.000 0.200 20.000 IMA Infinity 0.401

[0079]FIG. 11 illustrates a broad band design having approximately 26 mmdiameter, a wavelength of between approximately 266 and 313 nm, fieldsize of approximately 0.28 mm, and NA of approximately 0.90. The lensprescription for this design is shown in Table 9. TABLE 9 Prescriptionfor lenses for the design of FIG. 11 Surf Radius Thickness GlassDiameter OBJ Infinity Infinity 0.000 1.000 Infinity 19.109 8.783 STOInfinity −19.109 7.500 3.000 59.725 1.500 F_SILICA 8.772 4.000 −337.5791.500 8.650 5.000 −9.464 1.500 F_SILICA 8.574 6.000 −9.415 4.925 8.9007.000 8.637 1.200 F_SILICA 7.651 8.000 4.897 2.128 6.903 9.000 214.3491.750 F_SILICA 7.117 10.000 −12.598 1.147 7.334 11.000 −7.560 1.000F_SILICA 7.320 12.000 −772.023 0.100 7.974 13.000 9.411 2.000 F_SILICA8.548 14.000 −56.012 0.099 8.529 15.000 7.107 2.750 F_SILICA 8.35216.000 −22.495 1.159 7.805 17.000 −7.960 1.499 F_SILICA 7.103 18.000−10.073 5.482 6.716 19.000 3.034 1.748 F_SILICA 2.380 20.000 −20.1210.245 1.276 21.000 Infinity 1.041 0.955 22.000 16.855 4.806 F_SILICA26.000 23.000 11.392 6.422 20.000 24.000 −133.502 2.000 F_SILICA 20.00025.000 −100.000 −2.000 MIRROR 20.000 26.000 −133.502 −6.422 20.00027.000 11.392 −4.806 F_SILICA 20.000 28.000 16.855 4.806 MIRROR 26.00029.000 11.392 6.422 20.000 30.000 −133.502 2.000 F_SILICA 20.000 31.000−100.000 0.200 20.000 IMA Infinity 0.283

[0080] The current invention is capable of similar or better performanceover previously known catadioptric objectives with smaller maximum lensdiameters. The lens having the largest diameter in these designs istypically the highly curved Mangin mirror element, the second opticalelement from the object or specimen.

[0081] Designs similar to the objective shown in FIG. 2 have 0.9 NA,large corrected bandwidths using large optical elements, and relativelytight manufacturing tolerances. The current designs presented abovedisplay large corrected bandwidths but use relatively small opticalelements, and the designs have loose manufacturing tolerances. FIG. 12is a graph contrasting previous systems against the current design interms of relative bandwidth and maximum lens diameter. Relativebandwidth is defined as the bandwidth of the objective divided by thecenter wavelength. Previous systems are well corrected for relativebandwidths of at least 0.5 using lenses with maximum diameters greaterthan 100 mm. Current objective designs as presented herein use a singleglass material and are self corrected up to approximately 0.16 usinglenses with maximum diameters from around 20 mm up to 100 mm. Furthercorrection of these objectives over relative bandwidths up to 0.5 arepossible using tube lenses to correct residual chromatic aberrations asin the designs of FIGS. 7A and 7B. Similar correction is also possiblefor the objective alone by restricting NA or field size requirements.

[0082]FIG. 13 is a graph contrasting previous designs and the presentdesign in terms of field size and maximum lens diameter. Previoussystems tend to be well corrected for field sizes of 1 mm using lenseswith maximum diameters greater than 100 mm. Current objectives using thedesigns presented herein are corrected for field sizes of 0.4 mm usinglenses with maximum diameters from around 25 mm, and 1.0 mm field sizesusing lens diameters of 58 mm. From this and the graph of FIG. 12, theratio between field size and diameter of the largest element (includingthe Mangin mirror arrangement, field lens(es), and focusing lens(es), isgenerally less than 100 to 1, and may be less than 60 to 1. For example,the 58 mm lens diameter versus the 1.0 mm field size produces a ratio of58 to 1. Larger field sizes are also possible with increasing lensdiameter. Further correction of these objectives over larger field sizesare possible using tube lenses to correct residual chromatic aberrationsas in the designs of FIGS. 7A and 7B. Similar correction is alsopossible for the objective alone by restricting NA or bandwidthrequirements.

[0083] The present design may be employed in various environments,including but not limited to lithography, microscopy, biologicalinspection, medical research, and the like.

[0084] The design presented herein and the specific aspects illustratedare meant not to be limiting, but may include alternate components whilestill incorporating the teachings and benefits of the invention, namelythe small design having a high NA able to be employed in variouswavelengths using different illumination modes. While the invention hasthus been described in connection with specific embodiments thereof, itwill be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptations of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within known and customary practice withinthe art to which the invention pertains.

What is claimed is:
 1. An objective employed for use with light energyhaving a wavelength in the range of approximately 285 to 320 nanometers,comprising: a focusing lens group comprising at least one focusing lensconfigured to receive said light energy; a field lens oriented toreceive focused light energy from said focusing lens group and provideintermediate light energy; and a Mangin mirror arrangement positioned toreceive the intermediate light energy from the field lens and formcontrolled light energy; wherein a ratio of lens diameter for a largestelement of all focusing lenses, the field lens, and the Mangin mirrorarrangement to field size is less than 100 to
 1. 2. The objective ofclaim 1, said Mangin mirror arrangement comprising: a concavelens/mirror element having substantially curved concave surfaces andsecond surface reflectivity; and a relatively flat lens/mirror elementhaving minimally curved surfaces and second surface reflectivity.
 3. Theobjective of claim 1, configured to have a numerical aperture ofapproximately 0.9.
 4. The objective of claim 1, wherein each lens has adiameter of less than approximately 25 millimeters.
 5. The objective ofclaim 1, wherein said objective has a field size of approximately 0.28millimeters.
 6. The objective of claim 1, wherein said objective has afield size of approximately 0.40 millimeters.
 7. The objective of claim1, wherein all lenses are constructed of a single glass material.
 8. Theobjective of claim 1, said objective used with a microscope having aflange, wherein the flange may be located approximately 45 millimetersfrom the specimen, thereby providing reasonable optical resolution. 9.The objective of claim 1, said objective used with a microscope having aflange, wherein the flange may be located approximately 100 millimetersfrom the specimen, thereby providing reasonable optical resolution. 10.The objective of claim 1, wherein said focusing lens group comprisingsix focusing lenses.
 11. The objective of claim 1, wherein said fieldlens forms an intermediate image between said field lens and said Manginmirror arrangement.
 12. The objective of claim 1, wherein said objectivereceives light energy reflected back from said specimen through saidMangin mirror arrangement, said field lens, and said focusing lensgroup.
 13. The objective of claim 1, wherein ratio of lens diameter forthe largest element of all focusing lenses, the field lens, and theMangin mirror arrangement to field size is less than 75 to
 1. 14. Theobjective of claim 13, wherein ratio of lens diameter for the largestelement of all focusing lenses, the field lens, and the Mangin mirrorarrangement to field size is less than 60 to
 1. 15. An objectiveemployed for use with light energy having a wavelength in the range ofapproximately 157 nanometers through the infrared light range,comprising: a focusing lens group configured to receive said lightenergy and comprising at least one focusing lens; at least one fieldlens oriented to receive focused light energy from said focusing lensgroup and provide intermediate light energy; and a Mangin mirrorarrangement positioned to receive the intermediate light energy from thefield lens and form controlled light energy, said Mangin mirrorarrangement imparting the controlled light energy to a specimen with anumerical aperture in excess of 0.65, wherein each lens employed in theobjective and each element in the Mangin mirror arrangement has diameterless than 100 millimeters.
 16. The objective of claim 15, said Manginmirror arrangement comprising: a concave lens/mirror element havingsubstantially curved concave surfaces and second surface reflectivity;and a relatively flat lens/mirror element having minimally curvedsurfaces and second surface reflectivity.
 17. The objective of claim 15,said objective having a field size, wherein a of ratio lens diameter fora largest element of all focusing lenses, each field lens, and theMangin mirror arrangement to field size is less than 100 to
 1. 18. Theobjective of claim 17, wherein the of ratio lens diameter for a largestelement of all focusing lenses, each field lens, and the Mangin mirrorarrangement to field size is less than 75 to
 1. 19. The objective ofclaim 18, wherein the of ratio lens diameter for a largest element ofall focusing lenses, each field lens, and the Mangin mirror arrangementto field size is less than 60 to
 1. 20. The objective of claim 15,wherein each lens has a diameter of less than approximately 25millimeters.
 21. The objective of claim 15, wherein said objective has afield size of approximately 0.28 millimeters.
 22. The objective of claim15, wherein said objective has a field size of approximately 0.40millimeters.
 23. The objective of claim 15, wherein all lenses areconstructed of a single glass material.
 24. The objective of claim 15,said objective used with a microscope having a flange, wherein theflange may be located proximate the specimen, thereby providingreasonable optical resolution.
 25. The objective of claim 15, saidobjective used with a microscope having a flange, wherein the flange maybe located between approximately 45 and approximately 100 millimetersfrom the specimen, thereby providing reasonable optical resolution. 26.The objective of claim 15, configured to have a numerical aperture ofapproximately 0.9.
 27. An objective constructed of a single glassmaterial for use with light energy having a wavelength in the range ofapproximately 157 nanometers through the infrared light range,comprising: at least one focusing lens having diameter less thanapproximately 100 millimeters receiving said light energy andtransmitting focused light energy; at least one field lens havingdiameter less than approximately 100 millimeters, receiving said focusedlight energy and transmitting intermediate light energy; and at leastone Mangin mirror element having diameter less than 100 millimetersreceiving said intermediate light energy and providing controlled lightenergy to a specimen.
 28. The objective of claim 27, said at least oneMangin mirror element comprising: a concave lens/mirror element havingsubstantially curved concave surfaces and second surface reflectivity;and a relatively flat lens/mirror element having minimally curvedsurfaces and second surface reflectivity.
 29. The objective of claim 27,said objective having a field size, wherein a of ratio lens diameter fora largest element of all focusing lenses, each field lens, and theMangin mirror element to field size is less than 100 to
 1. 30. Theobjective of claim 29, wherein the of ratio lens diameter for a largestelement of all focusing lenses, each field lens, and the Mangin mirrorelement to field size is less than 75 to
 1. 31. The objective of claim30, wherein the of ratio lens diameter for a largest element of allfocusing lenses, each field lens, and the Mangin mirror element to fieldsize is less than 60 to
 1. 32. The objective of claim 27, configured tohave a numerical aperture of approximately 0.9.
 33. The objective ofclaim 27, wherein each lens has a diameter of less than approximately 25millimeters.
 34. The objective of claim 27, wherein said objective has afield size of approximately 0.28 millimeters.
 35. The objective of claim27, wherein said objective has a field size of approximately 0.40millimeters.
 36. The objective of claim 27, said objective used with amicroscope having a flange, wherein the flange may be located proximatethe specimen and use of the objective in the flange provides reasonableoptical resolution.
 37. The objective of claim 27, said objective usedwith a microscope having a flange, wherein the flange may be located ina range between approximately 45 and approximately 100 millimeters fromthe specimen, thereby providing reasonable optical resolution.
 38. Asystem for imaging a specimen using light energy in the range of 157nanometers through the infrared light range, comprising: a plurality oflenses having diameter of less than approximately 25 millimetersreceiving the light energy and providing intermediate light energy; anda Mangin mirror arrangement receiving the intermediate light energy andproviding controlled light energy to the specimen.
 39. The system ofclaim 38, wherein said plurality of lenses comprise: a focusing lensgroup comprising a plurality of focusing lenses, said focusing lensgroup receiving said light energy and providing focused light energy;and a field lens group comprising at least one field lens, said fieldlens group receiving the focused light energy and providing theintermediate light energy.
 40. The system of claim 38, said Manginmirror arrangement comprising: a concave lens/mirror element havingsubstantially curved concave surfaces and second surface reflectivity;and a relatively flat lens/mirror element having minimally curvedsurfaces and second surface reflectivity.
 41. The system of claim 39,wherein said system has a field size, wherein a of ratio lens diameterfor a largest element of all focusing lenses, each field lens, and theMangin mirror arrangement to field size is less than 100 to
 1. 42. Thesystem of claim 41, wherein the of ratio lens diameter for a largestelement of all focusing lenses, each field lens, and the Mangin mirrorarrangement to field size is less than 75 to
 1. 43. The system of claim41, wherein the of ratio lens diameter for a largest element of allfocusing lenses, each field lens, and the Mangin mirror arrangement tofield size is less than 60 to
 1. 44. The system of claim 38, configuredto have a numerical aperture of approximately 0.9.
 45. The system ofclaim 38, wherein said system has a field size of approximately 0.28millimeters.
 46. The system of claim 38, wherein said system has a fieldsize of approximately 0.40 millimeters.
 47. The system of claim 38, saidsystem used with a microscope having a flange, wherein the flange may belocated proximate the specimen, thereby providing reasonable opticalresolution.
 48. The system of claim 38, said system used with amicroscope having a flange, wherein the flange may be located in a rangebetween approximately 45 and approximately 100 millimeters from thespecimen, thereby providing reasonable optical resolution.
 49. Acatadioptric objective comprising: a catadioptric group comprising atleast one element configured to receive light energy from a specimen andproviding reflected light energy forming reflected light energy; a fieldlens group comprising at least one field lens receiving the reflectedlight energy and transmitting resultant light energy; and a focusinglens group comprising at least one focusing lens receiving resultantlight energy and transmitting focused resultant light energy, wherein animaging numerical aperture for the objective is at least 0.65, theobjective having a maximum lens diameter for all lenses employed and afield size, and wherein the ratio of maximum lens diameter to field sizeis less than 100 to
 1. 50. The objective of claim 49, wherein each lensis formed of fused silica.
 51. The objective of claim 49, wherein atleast one lens is formed of calcium fluoride.
 52. The objective of claim49, wherein lenses are formed from one from a group comprising fusedsilica and calcium fluoride.
 53. The objective of claim 49, where thecatadioptric group has less than 20 waves of on axis sphericalaberration.
 54. The objective of claim 53, wherein a decenter of anyelement by 0.01 mm reduces an associated wavefront by no more then 0.35rms waves at a worst field point.
 55. The objective of claim 49, whereina corrected bandwidth of the objective is at least 10 nm.
 56. Theobjective of claim 49, wherein a corrected bandwidth of the objective isat least 50 nm.
 57. The objective of claim 49, wherein a correctedbandwidth of the objective includes 313 nm.
 58. The objective of claim49, wherein a corrected bandwidth of the objective includes 266 nm. 59.The objective of claim 49, the objective having a field, wherein awavefront error is less than 0.1 waves RMS over the field.
 60. Theobjective of claim 49, the objective having a field, wherein the fieldis approximately 0.28 mm in diameter.
 61. The objective of claim 49, theobjective having a field, wherein the field is approximately 0.4 mm indiameter.
 62. A method of imaging a specimen, comprising: focusingreceived light energy using a focusing lens group; receiving focusedlight energy and providing intermediate light energy using a field lensgroup; and receiving intermediate light energy and forming controlledlight energy using a Mangin mirror arrangement; wherein a field size isformed using the focusing lens group, the field lens group, and theMangin mirror arrangement, and wherein a ratio of a largest element inthe focusing lens group, field lens group, and Mangin mirror arrangementto field size is less than 100 to
 1. 63. The method of claim 62, saidmethod being employed in the field of microscopy.
 64. The method ofclaim 62, said method being employed in the field of semiconductor waferinspection.
 65. The method of claim 62, said method being employed inthe field of lithography.
 66. The method of claim 62, said method beingemployed in the field of biological inspection.
 67. The method of claim62, said method being employed in the field of medical research.
 68. Themethod of claim 62, wherein the ratio of the largest element in thefocusing lens group, field lens group, and Mangin mirror arrangement tofield size is less than 75 to
 1. 69. The method of claim 62, wherein theratio of the largest element in the focusing lens group, field lensgroup, and Mangin mirror arrangement to field size is less than 60 to 1.70. The method of claim 62, wherein a largest element in the focusinglens group, field lens group, and Mangin mirror arrangement has diameterof less than 100 mm.
 71. An objective, comprising: means for focusingreceived light energy using a focusing lens group; means for receivingfocused light energy and providing intermediate light energy using afield lens group; and means for receiving intermediate light energy andforming controlled light energy using a Mangin mirror arrangement;wherein a field size is formed using the focusing lens group, the fieldlens group, and the Mangin mirror arrangement, and wherein a ratio of alargest element in the focusing lens group, field lens group, and Manginmirror arrangement to field size is less than 100 to
 1. 72. Theobjective of claim 71, said objective being employed in the field ofmicroscopy.
 73. The objective of claim 71, said objective being employedin the field of semiconductor wafer inspection.
 74. The objective ofclaim 71, wherein the ratio of the largest element in the focusing lensgroup, field lens group, and Mangin mirror arrangement to field size isless than 75 to
 1. 75. The objective of claim 71, wherein the ratio ofthe largest element in the focusing lens group, field lens group, andMangin mirror arrangement to field size is less than 60 to
 1. 76. Theobjective of claim 71, wherein a largest element in the focusing lensgroup, field lens group, and Mangin mirror arrangement has diameter ofless than 100 mm.
 77. A tube lens arrangement for use in correctingresidual aberrations in an objective, comprising: at least one focusinglens receiving light energy and focusing preliminary light energy to aninternal field; at least one field lens in proximity to the internalfield; and at least one conversion lens receiving the light energy fromthe internal field and transmitting light to a pupil.
 78. The objectiveof claim 1, wherein said objective has a field size of approximately 1millimeters.
 79. The objective of claim 15, wherein said objective has afield size of approximately 1 millimeters.
 80. The objective of claim27, wherein said objective has a field size of approximately 1millimeters.
 81. The system of claim 38, wherein said objective has afield size of approximately 1 millimeters.
 82. The objective of claim49, wherein said objective has a field size of approximately 1millimeters.
 83. The objective of claim 7 where the single glassmaterial is fused silica.
 84. The objective of claim 23 where the singleglass material is fused silica.
 85. The objective of claim 23 where thesingle glass material is calcium fluoride.
 86. The objective of claim 1where corrected bandwidth for the objective is less than approximately0.15.
 87. The objective of claim 15 where corrected bandwidth for theobjective is less than approximately 0.15.
 88. The objective of claim 27where corrected bandwidth for the objective is less than approximately0.15.
 89. The system of claim 38 where corrected bandwidth for theobjective is less than approximately 0.15.
 90. The objective of claim 39where corrected bandwidth for the objective is less than approximately0.15.
 91. The objective of claim 77 where two glass materials are used.92. The objective of claim 91 where the two glass materials are fusedsilica and calcium fluoride.
 93. The objective of claim 77 where thetube lens is optimized to correct the residual aberrations in a selfcorrected objective.
 94. The objective of claim 93 where the tube lensis optimized to increase field size.
 95. The objective of claim 93 wherethe tube lens is optimized to increase bandwidth.
 96. The objective ofclaim 94 where the field size is increased 25%.
 97. The objective ofclaim 93 where relative bandwidth is increased to approximately 0.25.98. The objective of claim 93 where relative bandwidth is increased toapproximately 0.35.
 99. The objective of claim 77 where the objectiveand tube lens are optimized together to correct for residualaberrations.
 100. The objective of claim 99 where relative bandwidth isincreased to approximately 0.5.
 101. The objective of claim 1, theobjective having a numerical aperture associated therewith, wherein thenumerical aperture is reduced to allow for increased field size. 102.The objective of claim 1, the objective having a numerical apertureassociated therewith, wherein the numerical aperture is reduced to allowfor increased relative bandwidth.
 103. The objective of claim 15, theobjective having a numerical aperture associated therewith, wherein thenumerical aperture is reduced to allow for increased field size. 104.The objective of claim 15, the objective having a numerical apertureassociated therewith, wherein the numerical aperture is reduced to allowfor increased relative bandwidth.
 105. The objective of claim 27, theobjective having a numerical aperture associated therewith, wherein thenumerical aperture is reduced to allow for an increase in field size.106. The objective of claim 27, the objective having a numericalaperture associated therewith, wherein the numerical aperture is reducedto allow for increased relative bandwidth.
 107. The objective of claim1, wherein maximum optical path error from a 10 micron decenter of anylens is less than approximately 0.12 microns.
 108. The objective ofclaim 1, wherein maximum optical path error from a 10 micron decenter ofeach lens is employed to form an average, and the average is less thanapproximately 0.08 microns.
 109. The objective of claim 13 whereinmaximum optical path error from a 10 micron decenter of any lens is lessthan approximately 0.12 microns.
 110. The objective of claim 13 whereinmaximum optical path error from a 10 micron decenter of each lens isemployed to form an average, and the average is less than approximately0.08 microns.
 111. The objective of claim 27 wherein maximum opticalpath error from a 10 micron decenter of any lens is less thanapproximately 0.12 microns.
 112. The objective of claim 27 whereinmaximum optical path error from a 10 micron decenter of each lens isemployed to form an average and the average is less than approximately0.08 microns.
 113. The system of claim 38 wherein maximum optical patherror from a 10 micron decenter of any lens is less than approximately0.12 microns.
 114. The system of claim 38 wherein maximum optical patherror from a 10 micron decenter of each lens is employed to form anaverage and the average is less than approximately 0.08 microns. 115.The objective of claim 49 wherein maximum optical path error from a 10micron decenter of any lens is less than approximately 0.12 microns.116. The objective of claim 49 wherein maximum optical path error from a10 micron decenter of each lens is employed to form an average and theaverage is less than approximately 0.08 microns.
 117. An objectiveemployed for use with light energy having a wavelength in the range ofapproximately 157 nanometers through the infrared light range,comprising: focusing means for receiving said light energy and providingfocused light energy; field lensing means for receiving focused lightenergy from said focusing means and providing intermediate light energy;and mirror means for receiving the intermediate light energy from thefield lensing means and forming controlled light energy, said mirrormeans imparting the controlled light energy to a specimen with anumerical aperture in excess of 0.65, wherein each lens employed in theobjective and each element in the mirror means has diameter less than100 millimeters.